Merge branch 'ak/commit-only-allow-empty'

"git commit --allow-empty --only" (no pathspec) with dirty index
ought to be an acceptable way to create a new commit that does not
change any paths, but it was forbidden, perhaps because nobody
needed it so far.

* ak/commit-only-allow-empty:
  commit: remove 'Clever' message for --only --amend
  commit: make --only --allow-empty work without paths

Documentation/git-commit.txt

@@ -265,7 +265,8 @@ FROM UPSTREAM REBASE" section in linkgit:git-rebase[1].)
 	If this option is specified together with `--amend`, then
 	no paths need to be specified, which can be used to amend
 	the last commit without committing changes that have
-	already been staged.
+	already been staged. If used together with `--allow-empty`
+	paths are also not required, and an empty commit will be created.
 
 -u[<mode>]::
 --untracked-files[=<mode>]::